Mn-doped ZnO Thin Films Research Articles

Influence of postdeposition annealing on the structural and optical properties of cosputtered Mn doped ZnO thin films

The influence of postgrowth annealing on the structural and optical properties of rf cosputtered Mn doped ZnO thin films deposited on glass substrate at room temperature has been investigated. All as deposited Zn1−xMnxO films are highly textured, with the c axis of the wurtzite structure along the growth direction. The as grown films are in a state of compressive stress and a reduction in stress with postgrowth annealing treatment are observed. The band gap of Mn doped ZnO films (3.34eV) is slightly larger than the pure ZnO film (3.30eV) and is found to decrease with an increase in annealing temperature for all the samples. The optical dispersion of refractive index with photon energy in Zn1−xMnxO films with varying x and different annealing temperature is studied in the light of single oscillator and Pikhtin-Yas’kov [Sov. Phys. Semicond. 15, 81 (1981)] model, respectively.

Room-temperature ferromagnetic ordering in Mn-doped ZnO thin films grown by pulsed laser deposition

The ferromagnetic ordering in Mn-doped ZnO thin films grown by pulsed laser deposition (PLD) as a function of oxygen pressure and substrate temperature has been investigated. Room-temperature ferromagnetic behaviors in the Mn-doped ZnO films grown at 700°C and 800°C under 10−1 torr in oxygen pressure were found, whereas ferromagnetic ordering in the films grown under 10−3 torr disappeared at 300 K. The large positive magnetoresistance (MR), ∼10%, was observed at 5 K at low fields and small negative MR was observed at high fields, irrespective of oxygen pressure. In particular, anomalous Hall effect (AHE) in the Mn-doped ZnO film grown at 700°C under 10−1 Torr has been observed up to 210 K. In this work, the observed AHE is believed to be further direct evidence demonstrating that the Mn-doped ZnO thin films are ferromagnetic.

Structural, optical, and magnetic properties of Mn-doped ZnO thin film

The Zn(1-x)Mn(x)O (x = 0, 0.16, and 0.25) thin films were grown on fused quartz substrates by reactive magnetron cosputtering. X-ray-diffraction measurement revealed that all the films were single phase and had wurtzite structure with c-axis orientation. As Mn concentration increased in the Zn(1-x)Mn(x)O films, the c-axis lattice constant and band-gap energy increased gradually. In Raman-scattering studies, an additional Mn-related vibration mode appeared at 520 cm(-1). E(2H) phonon line of Zn(1-x)Mn(x)O alloy was broadened asymmetrically and redshifted as a result of microscopic structural disorder induced by Mn(2+) random substitution. The Zn(0.84)Mn(0.16)O film exhibited a ferromagnetic characteristic with a Curie temperature of approximately 62 K. However, with increasing Mn concentration to 25 at. %, ferromagnetism disappeared due to the enhanced antiferromagnetic superexchange interactions between neighboring Mn(2+) ions.

Structure and optical properties of Mn doped ZnO thin films

Mn-doped ZnO thin films were prepared on SiO2 substrate using pulsed laser deposition (PLD) technique in order to investigate the structure and optical properties of the films. XRD, AFM, EDX analysis and UV-VIS spectrophotometry were employed to characterize the Mn-doped ZnO films. The results showed that the shape of the XRD spectrum was remarkably similar to that of the un-doped ZnO film, indicating that the structure of the films was not disturbed by Mn-doping and the film also had mainly (103) peaks. The contents of (Zn, Mn)O thin films prepared by PLD were consistent with the targets, thus realizing the thin films deposition with same constitutuents as the target. The films had rather flat surfaces with the peak-to-tail roughness of about 80nm and an average grain diameter of about 25nm. Mn-doping changed the band gap of the films, which increased with the increase of the Mn content. Moreover, when the Mn content increased from 6% to 12%，the absorbence in strong UV absorption band increased too.

Magnetic and optical properties of Zn 1−xMn xO thin films prepared by pulsed laser deposition

We report on ferromagnetic characteristics of Zn 1− x Mn x O thin films grown on Al 2O 3 substrates by using pulsed laser deposition. The effects of oxygen pressure on the ferromagnetism in the Mn-doped ZnO thin films are discussed. The carrier concentration was found to be controlled by varying the oxygen pressure. By decreasing oxygen pressure, the films exhibited increases in both the lattice constant and fundamental band gap energy. Large magnetoresistance (MR) was observed in the film grown at 700 °C, especially over 10% in the positive MR. The results indicate the spin splitting caused by strong s–d exchange coupling between the conducting carriers and localized spins of Mn ions.

Structural analysis of ferromagnetic Mn-doped ZnO thin films deposited by radio frequency magnetron sputtering

We report on the structural analysis of ferromagnetic Mn-doped ZnO thin films deposited by radio frequency magnetron sputtering, using transmission electron microscopy (TEM), high-resolution x-ray diffraction, and Rutherford backscattering spectroscopy (RBS) measurements. The ferromagnetic Mn-doped ZnO film showed magnetization hysteresis at 5 and 300K. A TEM analysis revealed that the Mn-doped ZnO included a high density of round-shaped cubic and elongated hexagonal MnZn oxide precipitates. The incorporation of Mn caused a large amount of structural disorder in the crystalline columnar ZnO lattice, although the wurtzite crystal structure was maintained. The observed ferromagnetism is discussed based on the structural characteristics indicated by TEM and the behavior of Mn when it is substituted into a ZnO lattice derived from RBS measurements.

Magnetization dependence on electron density in epitaxial ZnO thin films codoped with Mn and Sn

The magnetic and transport properties of Mn-doped ZnO thin films codoped with Sn are examined. Superconducting quantum interference device magnetometry measurements indicate that the films are ferromagnetic with an inverse correlation between magnetization and electron density as controlled by Sn doping. Magnetism in low free-electron density material is consistent with the bound magnetic polaron model, in which bound acceptors mediate the ferromagnetic ordering. Increasing the electron density decreases the acceptor concentration, thus quenching the ferromagnetic exchange. This result is important in understanding ferromagnetism in transition-metal-doped semiconductors for spintronic devices.

UV optical properties of ferromagnetic Mn-doped ZnO thin films grown by PLD

The incorporation of 3d transition metals into ZnO can produce ferromagnetism above room temperature. For Mn-doped ZnO films grown at low temperatures around 500 °C by pulsed laser deposition, the ferromagnetic behavior is correlated to their textured structure. For optimized films showing homogeneous magnetic domain formation in magnetic force microscopy, the saturation magnetization and coercive field strength amount to 0.013 emu/g and 234 Oe at 300 K, respectively. Compared to undoped ZnO films, the luminescence of Mn-doped ZnO films is strongly quenched. However, luminescence can be observed around antiferromagnetic MnO or MnO 2 clusters that crystallize during the growth process on the film surface.

Epitaxial Growth of Mn-Doped ZnO Thin Films on Al<sub>2</sub>O<sub>3</sub> (0001)

Growth behavior of Mn-doped ZnO thin films (Zn1-xMnxO) onAl2O3 (0001) substrates by pulsed laser deposition was investigated as a function of Mn content (0.00≤x≤0.35) mainly using synchrotron x-ray diffraction. We found that a small amount of Mn doping (x=0.05) significantly improves the crystalline quality, and also leads to a singly oriented film. The superior epitaxial growth of the film with an optimum Mn content seems to be associated with its microstructural evolution.

Heteroepitaxial growth behavior of Mn-doped ZnO thin films on Al2O3 (0001) by pulsed laser deposition

Heteroepitaxial growth behavior of Mn-doped ZnO thin films (Zn1−xMnxO) on Al2O3 (0001) substrates by pulsed laser deposition was investigated particularly as a function of Mn content (0.00⩽x⩽0.35) using synchrotron x-ray scattering and atomic force microscopy. The undoped ZnO film was grown epitaxially with a 30° rotation of ZnO basal planes with respect to the Al2O3 substrate while having a small amount of grains with another epitaxial relationship, i.e., the hexagon-on-hexagon growth. A small amount of Mn doping (x=0.05) not only greatly improved the atomic alignment both in the in-plane and in the out-of-plane directions, but also led to a singly oriented film by totally suppressing the hexagon-on-hexagon growth. With further incorporation of Mn into ZnO beyond that content, the epitaxial nature again deteriorated. The superior epitaxial growth of the film with an optimum Mn content is attributed to the formation of much larger grains in it. In addition, our Mn-doped ZnO thin films showed a paramagnetic behavior.

Electro-optic effect in ZnO:Mn thin films

The electro-optic effect of ZnO epitaxial films was studied. Since the electro-optic effect in ZnO is inferior to that of ferroelectric materials, an increase in the electro-optic effect was expected in ZnO having ferroelectricity, due to the increase in the dielectric constant. Although Li and Mg doped ZnO film exhibited electro-optic response, the mobile Li ions influenced the polarization behaviour. To eliminate the electro-optic effect induced by other space charge effects, the birefringence shift measurement was performed. The measurement with ac electric field at various frequencies could abstract the electro-optic effect of Mn-doped ZnO thin films induced only by dipolar polarizability.

Transparent conductive Al and Mn doped ZnO thin films prepared by DC reactive magnetron sputtering

ZnO films doped with Al and Mn have been prepared by DC reactive magnetron sputtering at room temperature. The electro-optical, structural properties and compositional analysis of the films have been investigated using Hall-effect measurement, optical spectroscopy, X-ray diffraction, atomic force microscope and Auger electron spectroscopy. A minimum resistivity of 3.46×10−4 Ω cm and more than 80.0% transmittance at 550 nm have been obtained. It has been observed that the percentages of Al and Mn in the films were slightly lower than that of Al and Mn mixed in the targets. It has been found that all deposited films, which contains compressive stress, have c-axis preferred orientation perpendicular to the substrate with flat and smooth surface (root-mean-square surface roughness is of the order of ∼3 nm over 5×5 μm2). In-grain scattering has been suggested to be the most probable scattering mechanism for the films (N>1020 cm−3) at room temperature.

Transparent conductive Al and Mn doped ZnO thin films prepared by DC reactive magnetron sputtering

ZnO films doped with Al and Mn have been prepared by DC reactive magnetron sputtering at room temperature. The electro-optical, structural properties and compositional analysis of the films have been investigated using Hall-effect measurement, optical spectroscopy, X-ray diffraction, atomic force microscope and Auger electron spectroscopy. A minimum resistivity of 3.46×10 −4 Ω cm and more than 80.0% transmittance at 550 nm have been obtained. It has been observed that the percentages of Al and Mn in the films were slightly lower than that of Al and Mn mixed in the targets. It has been found that all deposited films, which contains compressive stress, have c-axis preferred orientation perpendicular to the substrate with flat and smooth surface (root-mean-square surface roughness is of the order of ∼3 nm over 5×5 μm 2). In-grain scattering has been suggested to be the most probable scattering mechanism for the films ( N>10 20 cm −3) at room temperature.

Magnetism in Mn-doped ZnO bulk samples prepared by solid state reaction

Contrasting magnetic properties were obtained from bulk Mn-doped ZnO synthesized under different processing conditions. While a ferrimagnetic phase transition was observable in a Zn0.95Mn0.05O sample processed at 1170 K, no such transition was found for a sample with the same composition processed at 1370 K. The detailed magnetic, structural, and spectroscopic studies of these two samples have revealed that the ferrimagnetic transition in the former sample is attributable to the secondary phase, (Mn,Zn)Mn2O4, in the system. For the latter sample processed at higher temperature, no secondary phase was detected and the major feature of the system remained paramagnetic down to 4 K. The implication of the present results for Mn-doped ZnO thin films is discussed.

Blue and ultraviolet cathodoluminescence from Mn-doped epitaxial ZnO thin films

Combinatorial laser molecular-beam epitaxy method was employed to fabricate epitaxial Zn1−xMnxO thin films in a high throughput fashion. Local structures around Mn were investigated for these c-axis-oriented epitaxial films by fluorescence x-ray absorption fine structure measurements. It was shown that Mn substitutionally replaces Zn in Zn1−xMnxO (x<0.22) films. Well-structured blue and ultraviolet cathodoluminescence peaks corresponding to the intra-d-shell transitions of Mn2+ were observed, especially for smaller x. The luminescence is quenched rapidly as x is increased. By comparing the relative absorption strength per mole Mn2+ with the statistical probability of isolated Mn2+, it was concluded that the quick decrement of isolated Mn2+ with increasing x is responsible for the severe suppression of the blue and ultraviolet luminescence.

Magnetic properties of epitaxial Mn-doped ZnO thin films

Epitaxial ZnO thin films doped with 7% Mn have been made by reactive rf magnetron sputtering onto (112_0) sapphire substrates at 400 °C. X-ray diffraction measurements reveal that the Zn0.93Mn0.07O film has a (0001) wurtzite single-crystal structure with a rocking curve width of 0.98°. UV–VIS absorption spectra show a band gap of 3.25 eV for pure ZnO films and 3.31 eV for the Zn0.93Mn0.07O film with states extending into the gap. The Auger electron spectroscopy shows homogeneous distribution of Mn in the film. The magnetic properties of the Zn0.93Mn0.07O film have been measured by a superconducting quantum interference device magnetometer at various temperatures with fields up to 5 T. No ferromagnetic ordering has been observed at temperature at 5 K. Instead, paramagnetic characteristics with a Curie–Weiss behavior have been observed.

Pulsed laser deposition of ZnO and Mn-doped ZnO thin films

Pulsed laser deposition has been used to prepare thin films of ZnO on (0 0 0 1) sapphire at 400 °C. The target-substrate distance and the background oxygen pressure were varied. A time-of-flight ion probe was used to investigate the interaction of the laser ablation plume with the background gas and measure the ion flux at the substrate. The film properties were measured using X-ray diffraction and photoluminescence spectroscopy. It has been shown that crystalline quality and the photoluminescence properties are better at higher oxygen pressures, which give a longer plasma residence time at the substrate.

Effect of Mn Doping in ZnO Thin Films Deposited by Pulsed Laser Deposition

AbstractMn doped ZnO thin films were grown using pulsed laser deposition technique on (001) Al2O3 substrates. The x-ray diffraction data confirmed highly c-axis oriented and hexagonal structure of ZnO and Mn doped ZnO thin films. However, an unidentified secondary peak was observed at very close to ZnO (002) peak. Micro Raman spectra of ceramics as well as thin films showed disorder induced Raman bands besides standard wurtzite ZnO modes. The intensity of several LO modes of ZnO was increased with the increase of Mn concentration. Optical absorption data showed an additional absorption band towards lower than bandgap energy (3 eV) with the increase in Mn content. The incorporation of Mn in ZnO thin films reduced the value of resistivities and mobilities with an increase in carrier concentrations.